Child Psychology. Jean-Pascal Assailly

girls outperform boys in grades and verbal performance in school and that boys’ averages exceed those of girls in spatial and mathematical tasks.

      Such differences have been documented in many countries, but have been found to be particularly prevalent in North America and economically developed countries.

      In the vast literature on this topic, relatively few studies have considered differences in the non-parental child care settings where boys and girls spend their early years. Yet more than three-quarters of preschoolers in the United States attend some type of non-parental child care and attendance is correlated with school readiness and achievement.

One study (Gordona 2020) showed gender differences in child care arrangements among preschoolers in the United States: in families of high socioeconomic status, boys were more likely than girls to attend centers, but the reverse was true in less affluent families. Parents’ general perspectives that center- or home-based child care is better for preschool development and safety also differed depending on whether the child studied was a boy or girl in families of varying socioeconomic status. Given that center-based child care attendance for preschoolers has been associated with school readiness, it is important to understand and address these gender disparities. It would be interesting to obtain data on this topic in France.

1.13. Ranking among siblings

      The first psychologist to study the influence of sibling rank was a psychoanalyst, Adler, who placed the feeling of inferiority at the heart of the creation of neurosis. He believed that sibling rivalry and the dominance of the eldest sibling are at the root of psychological differences between siblings. Freud, on the other hand, attributed little importance to sibling rank, as he gave much more importance to the emotional relationship with the parents. It must also be said that Adler lived at a time when the eldest sibling was indeed very much favored, particularly with regard to inheritance, so that there was no indivision.

      These privileges have disappeared today. On the other hand, what has not changed is the role of “opener”, to borrow a mountain metaphor, played by the eldest child and the task of inclusion into an already formed relational universe that falls to the youngest child. Sibling rank is therefore the variable that comes most naturally to mind when we think of the evolution of the structure and that of the non-shared family environment: the eldest is first alone, then has to “make way” for the youngest, the parents have more experience and so on.

      It has long been assumed that first-borns were first spoiled and then “dethroned”, which would constitute a form of trauma. In order to overcome this trauma, they would reinforce the imitation of their parents and the feeling of responsibility towards the younger children. They would thus put more emphasis on rule, discipline and become more conservative. First-borns who do not overcome this battle for the “lost love” of the mother become angry or resigned.

      For a long time, a different hypothesis was also assumed, that for first-borns, parents are inexperienced and are more anxious and more demanding in their parenting behavior. This would make the older children more fearful and more dependent (and possibly therefore more dependent on psychoactive substances?). The younger children would be more open, more independent and more rebellious, and the older ones would be more conformist, more ambitious, etc. The feelings of an only child would be closer to those of an older child than a younger one.

However, what do 50 years of research on sibling rank show? Well, they show that there is no correlation between sibling rank and personality, in particular, that we do not find the above associations with openness of mind. In fact, the results of the studies go in all directions, and analysts have not been lacking in imagination when explaining completely opposite results, based on the use of popular theories about the effects of rank, when it suits the reasoning.

      Associations with the subject’s personality traits are only found in descriptions by parents or siblings. In fact, the influence of sibling rank would only be subjective: the way others see you, the way you behave at home because “an older child is supposed to behave like this or like that”, but in no case does this translate objectively into measurements when taking personality tests.

1.14. Sibling size

      There is a stereotype of the only child (egocentric, tyrannical, etc.), but does this cliché correspond to reality? Studies on this topic have not found any particular characteristics of only children (Almodovar 1981). It is true that childhood experiences are different for only children, but we can imagine that relationships with parents and then with peers would create a strong psychological variability among these children.

      In China, the one-child policy in particular led to the belief that these only children were “little emperors”, corresponding to the stereotype.

      Male only children received fewer positive evaluations than female only children. In particular, they were found to be at greater risk of obesity.

      Evaluations of only children are better after the implementation of the one-child policy in 1979 than before, but the policy has just changed.

1.15. Twins

      The birth of twins is always a phenomenon that arouses curiosity. It is known that there are two types of twins: dizygotic twins resulting from the fertilization of two ovocytes by two different spermatozoa, and therefore have a different genetic heritage, like brothers and sisters; and monozygotic twins resulting from the division of a single embryo and therefore have an identical genetic heritage.

      The prevalence of twin births has increased over the past 40 years in France:

       – 1972: 9 births out of 1,000;

       – 2000: 15 births out of 1,000;

       – 2013: 17 births out of 1,000.

This increase is mostly related to dizygotic pregnancies, the prevalence of monozygotic pregnancies being stable at around 1 to 3 per 1,000 births.

      Prevalence varies according to culture: in Europe and the United States, the rates are between 10 and 20, in Asia 6 and in some African countries 40.

      Why this increase? Two factors have been put forward:

       – the increase in the age of the mother at first child, that we mentioned above;

       – the developments in medically assisted procreation. Thus, the proportion of twin births is 17% following in vitro fertilization, 9% following intrauterine insemination with the spouse’s sperm and 11% with donor sperm.

      1.15.1. Aspects of vulnerability

      Twins have greater morbidity and mortality than other children:

       – from the fetal period: intrauterine growth retardation (average weight of twins under 600 grams), TOPS (Twin Oliguria Polyhydramnios Syndrome, or acardiac twin, an anemia related to hemodynamic and hormonal imbalance in 5 to 15% of cases), congenital malformations (mainly heart disease, relative risk of 1.7), prematurity (in 43% of cases, or 7 times more frequent than for single pregnancies), perinatal anoxia (especially for the second twin);

       – higher neonatal mortality: in the EPIPAGE cohort study of low gestational ages (2,773 premature infants, before 32 weeks), the risk of death in hospital was increased for twins, after adjustment for gestational age and sex, and their survival at five years was decreased. Some factors influence this mortality, such as birth order or weight discrepancy (relative risk of 2.9 in the EPIPAGE study);

       – sudden infant death syndrome has been observed to be more frequent in twins, but this correlation no longer holds when birth weight, prematurity and sociodemographic data are controlled.

      These increased neonatal and perinatal risks in multiple pregnancies are no longer observed later in life (cancers and cardiovascular diseases are not more prevalent in twins).

      Regarding